This invention relates to an apparatus of and method for continuously reeling a web material of a paper machine. In particular, this invention relates to continuously reeling a paper web of a paper machine producing paper whose surface properties have been influenced by calendering the paper by using more than one calendering nip.
Traditionally high gloss magazine paper grades such as so called SC-A (Super Calendered Paper) paper has been produced by two stages: in a first stage producing a base paper, and in a second stage, calendering the base paper as a separate operation. For obtaining desired results the base paper has been produced traditionally as follows. The formation and press-drying of the paper web has been performed in a common way for those grades. However, the final solid content of the paper has been increased up to 97-99 per cent of the total mass in order to obtain an even cross directional web moisture profile. After that, the paper has been moisturized to be approximately in moisture content of 6-10 per cent of total paper weight, which is considered to be advantageous for the calendering process. The super calendering is then performed after a while in a separate stage independent from the paper machine where the base paper was manufactured.
Moisturizing or rewetting is possible, for instance with spray application units. An example of this is described in U.S. Pat. No. 5,286,348, the entire disclosure of which is incorporated herein by reference. In U.S. Pat. No. 5,286,348 is described a method for controlling the rewetting apparatus to get an even profile of moisture across the paper width. Rewetting is possible with a very good CD (cross directional) profile.
The problem of rewetting the paper after the drying section with this and other methods is the time needed for paper to absorb the applied water and equalize the moisture content in the direction of thickness and surface areas. If the rewetting is made just before the paper is calendered, the uneven distribution of moisture will affect the final surface properties of the produced paper and the quality grading of the paper will be lowered.
Because of the aforementioned effect in the paper, it is typically reeled up after rewetting and transferred to a waiting station for moisture equalization in the paper web, and then to off-line calenders which are able to produce high gloss and to densify the surface of the paper for final calendering.
Because it was not possible earlier to supercalender high gloss SC-A paper on-line there was no urgent need for improvement. In addition, traditionally supercalendered papergrades such as SC-A and LWC are calendered in two or even three off-line calenders at lower speeds than the papermachine speed to achieve the wanted finishing of the paper.
It has, however, been found that considerable advantages may be achieved by producing SC-paper by using a so called on-line multi-nip calender. This is described in more detail in a co-pending U.S. patent application Ser. No. 09/191,227 xe2x80x9cMethod for Producing High Gloss Magazine Paperxe2x80x9d filed on Nov. 13, 1998 and assigned to the assignee of the present application. The disclosure of the co-pending patent application is incorporated herein by reference, and it describes a process and a new on-line multi-nip calendering concept which makes it possible to also finish premium surface-finished printing paper grades like SCA or LWC grades without additional off-line calendering units, because it is possible to use additional calendering capacity compared to the traditional supercalendering process where nip load is a sum function of the weights of all calendering rolls above each nip and the additional load produced with the uppermost roll of the calendering stack. The concept of using additional calendering capacity is explained in the U.S. Pat. No. 5,438,920, the entire disclosure of which is incorporated herein by reference. This is particularly advantageous in on-line calendering because the additional calendering capacity may be used either for higher finishing or increased capacity of a papermachine.
In such a process or production concept it may be desirable to use, eg., following CD-profile actuators alternatively or simultaneously:
a profiling steam box in the press section controlled by CD-profile measurement(s) located after the profiling steam box, preferably after the first drying cylinder group, the measurements being preferably moisture profile measurements and/or tension profile measurements and/or temperature profile measurements;
a CD temperature adjustment in at least one, preferably the last (when only one), of the drying cylinder groups to achieve a uniform temperature profile in web cross direction controlled by a temperature profile measurement unit located after the CD temperature adjustment unit in or between drying cylinder groups or after the last drying cylinder group;
a moisture profile adjustment before the last drying cylinder group by profiling the drying cylinder surface temperatures and/or using profitable infrared drying units to adjust the moisture of the web and/or using rewetting equipment for profile corrections using the measuring of temperature and/or moisture profile of the web located in or after the last drying cylinder group;
cooling the web down to the temperature level of the machine hall or the drying section housing before the calendering unit to prevent the continuation of drying of the paper between the calender and the last drying equipment downstream of the headbox and thereby preventing the unequal moisture evaporation from the web before calendering;
final moisture profile levelling by applying water in the form of steam spray or thin film transferred in the paper in a calender nip or a possible surface sizing unit inside the drying cylinder group or between the last drying cylinder and the calender and controlled by web CD profile measurement located either immediatelly after or before the calender.
Also, the surface sizing unit can be used as a moisture profiler in connection with profile measurements mentioned earlier in this description. The preferable moisture before the first nip of the calender is between 7% and 20% calculated on the basis of the total weight of the web.
Also, it has been recently found that, especially in connection with on-line high gloss magazine paper production, there are some demands for reeling of on-line produced high-gloss magazine paper such as SC-A paper, which demands have not been present in reeling of the base paper or other paper grades. For example it has been found that a possible uneven thickness profile results in difficulties in the winding operation causing CD (cross directional) bumps or bands not only on machine rolls but possibly also on client paper rolls which has a negative effect on the runnability of paper in printing and converting machines.
In paper machines the reeling of web is traditionally performed by using a reel including a driven reeling cylinder over which the paper passes when reeled around a spool being in nip contact with the reeling cylinder. Typically the reeling cylinder is rotatably supported and the reel spool reeling the web is supported by two parallel rails extending in machine direction on both sides of the reel. The reel typically includes also so-called primary and secondary carriages (forks or arms). The reeling on a new reel spool is commenced on the primary carriages and after a certain desired time the secondary carriages take over the supporting of the reel spool and the roll. That kind of a reel is described for example in U.S. Pat. No. 5,251,835, the entire disclosure of which is incorporated herein by reference.
Typically the parameters being used for controlling the reeling process and influencing the results of the reeling are mainly the nip force between the reeling cylinder and the roll as well as the torque of the central-driven reel spool. It is also known to alter the nip force as a function of the roll diameter.
In this context the wording xe2x80x9con-line sc paper machinexe2x80x9d is used to stand for a paper machine concept including a wire section, press section, drying section and an on-line calender including more than one calendering nip which have a positive effect on the surface properties of paper.
In such a production line concept there is required a reliable reeling apparatus which provides a continuous operation (reeling/reel change) at operational speeds which typically nowadays exceed 1000 m/min.
It is an intention of the invention to minimize the drawbacks of the known methods. It is also an intention of the invention to minimize problems in reeling of on-line high-gloss magazine paper at a machine reel.
It is also an intention of the invention to provide an advantageous method for providing a reeling process in which the paper reeled on the reel spool will remain at a non-constant cross directional position over the reel spool.
In order to meet the demands set on a on-line sc paper machine as well as on a reeling process of the high-gloss magazine paper, the production line is provided with means of reeling the web on the reel spool of the reeling device at a non-constant cross directional position over the reel spool.
In accordance with a preferred embodiment of the invention in connection with an on-line sc paper machine, the paper machine comprises at least:
a forming section adapted to produce sc base paper web;
a press section adapted to water removal by pressing for production of sc base paper web
a drying section for evaporative drying of sc base paper;
means for controlling the production of the sc base paper to produce base paper capable of being calendered in an on-line multi nip calender;
an on-line calender unit producing high-gloss magazine paper;
paper web oscillating means providing cross directional substantially continuous alternating movement of the paper web after the on-line calender; and
a reel for reeling the calendered paper web.
In accordance with another embodiment of the invention, a continuous reel for reeling paper web produced in a paper production machine in connection with the reel is provided for producing a machine roll, the reel including at least:
a reeling cylinder for guiding paper web through a nip between the reeling cylinder and a reel spool at least in reeling position of the reel spool;
a pair of rails supporting at least the reel spool and the roll being reeled; and
means for providing a cross-directional, substantially continuous alternating cross directional roll formation position movement of the paper web around the reel spool.
According to a preferred embodiment of the invention, the means for providing the cross directional substantially continuous alternating cross directional roll formation position movement of the paper web around the reel spool comprise a guiding arrangement in the bearing housing of both ends of the reel spool which allows a suitable movement, in direction of the axis of the spool, between the reel spool and at least a section of the outer surface of the bearing housing. This is accomplished according to the invention by providing the bearing with an outer shell capable of controllably sliding in an axial direction.
The oscillating is arranged to take place so that during one oscillation cycle there is at least 100 m but preferably 200 m paper reeled on the roll. By reeling 200 m of paper during each oscillation cycle the quality of the roll is still maintained at a good level.
According to still another embodiment of the invention, the reel having carriages for supporting the reel spool and the roll are provided with means for holding the bearing housings of the reel spool, the means for holding being provided with guiding means which allow a suitable movement in direction of the axis of the spool.